PRIMULINE PROCESS.--A recent process invented by Messrs. Green, Cross and Bevan. It is better known, however, as the " Diazotye process." The following description of it is partly taken from a lecture given by the inventors*:- This process in reality consists of a new application of a group of colored compounds, of which the dyestuff known as primuline is the typical representative. Primuline is the sodium sulphonate of a complex amido base, which is obtained by heating paratoluidine with sulphur. Its formation is preceded by that of dehydrothiotoluidine, a body which appears to be an amido benzenyl-amidothiocresol, and the primuline base appears to result from a further condensation of this compound, and to differ from it in the same way that dehydrothiotoluidine itself differs from paratoluidine. This view is expressed in the formula for primuline proposed by Gattermann.
Homologues of primuline closely similar to it in properties are similarly obtained from metaxylidine and pseudo-cumidine.
In printing upon textile fabrics the material is first dyed with a hot solution of primuline, to which some common salt may be added. About fifteen to thirty grains of primuline are added to about a gallon of hot water. In this solution the fabric acquires a primrose-yellow color. It is then washed in cold water, and afterwards diazotized by immersion for about half a minute in a cold solution of sodium nitrite + per cent., which has been sharply acidified with hydrochloric, sulphuric, or other acid. The material is now washed in cold water and stretched out on a level white surface, and exposed to light beneath the object of which it is required to produce a posi tive reproduction. It is, of course, possible to print from ordinary photographic positives or from natural objects or from any painted, printed, or photographed design or picture upon any suffici ently transparent material. Either sunlight or an artificial light of sufficient intensity may be employed, the time of exposure, of course, varying with the intensity of the light. In printing by daylight it varies from half a minute in bright sunshine to half an hour or so in very dull weather.
When the decomposition of the diazo compound in the high lights of the picture is com plete (which can be easily ascertained by means of a test slip exposed simultaneously and touched with a solution of /3-naphthol, at intervals) these portions will be found to have changed from an orange to a pale yellow. The material is now either passed into the developing bath at once or is kept in the dark until it is convenient to develop the image. The developing bath consist of a weak solution (about .per cent.) of a suitable phenol or amine, depending upon the color in which the design is to be produced. The following phenols and amines, amongst others, have been found to give good results:— For Red, an alkaline solution of fi-naphthol. • For Maroon, an alkaline solution of a fi-naphthol disulphonic acid.
For Yellow, an alkaline solution of phenol.
For Orange, an alkaline solution of resorcin.
For Brown, a slightly alkaline solution of pyrogallol, or a solution of phenylenediamine hydrochl ori de.
For Purple, a solution of a-naphthylamine-hydrochloride.
For Blue, a slightly acid solution of amido-fi-naphthol-/3sulphonate of sodium (eikonogen).
If the design is desired to be produced in two or more colors the respective developers suitably thickened with starch, if necessary, may be applied locally by means of a pad or brush. After development, which with cotton is complete in less than half a minute, the material is washed, and the picture requires no further fixing. In the case of the purple and blue developers it is necessary to wash the material finally in a very weak solution of tartaric acid It is some times advantageous to heat for a few seconds in a hot soap bath.
Velveteen, linen, silk, wool, and other fabrics may be treated in the same manner except that in the case of wool and silk a longer exposure to light is necessary, and the immersion in the nitric and developing baths must also be more prolonged. The maroon and blue developers are not suitable for silk and wool.